Blackening copper alloys



Patented Dec. 28, 1948 UNITED STATES BLACKENING COPPER ALLOYS Earle B.Lewis, Southington, Conn.

N Drawing. Application April 19, 1945, Serial No. 589,267

Claims.

The present invention relates to a process for blackening copper alloyshaving substantial copper content.

There have been numerous oxidizing processes for producing a blackfinish on copper and copper alloys which involve the use of variousoxidizing agents.

The process which produces the most satisfactory finish and is mostcommonly used makes use of a solution composed of sodium or potassiumhydroxide and sodium or potassium chlorite dissolved in water, operatedat or near boiling temperature.

The normal procedure followed to oxidize the copper or copper alloyparts is to clean theparts of grease and dirt by any of the well-knownmeans, and then further clean the parts of surface impurities by etchingin a suitable etching solution.

After the surface preparation is complete, the parts are immersed in theoxidizing solution until a uniform black oxide is formed. Parts are thenrinsed and dried, after which oil or wax may be applied to improve theappearance.

Copper is very readily oxidizedby the method described, and copperalloys of very high copper content can also be so oxidized. However,copper alloys become increasingly difficult to satisfactorily oxidize asthe copper content of the alloy diminishes. ticularly to the oxidationof copper alloys wherein the copper content is substantial but isnevertheless too low to enable satisfactory oxidation to be attained byheretofore existing methods. Such alloys include brass, bronze, Phosphorbronze, Muntz metal and beryllium copper. The term copper base alloy isto be understood as designating an alloy such as those last abovereferred to.

Another difficulty exists in connection with the oxidization of somecopper alloys. For instance, when brass, with high copper that permitssatisfactory blackening, is processed, the zinc content of the brassrapidly weakens the oxidizing solution so that frequent renewal isnecessary which results in high finishing cost.

In order to overcome the difficulties above outlined, it has been commonpractice to copper plate copper alloys of the class described which weretroublesome and to then oxidize the copper plate.

The object of the present invention is to provide a process which willpermit the oxidization of copper alloys of the class described withoutcopper plating, and which will extend the life of The present inventionrelates parthe copper oxidizing solution when used for coloring copperalloys which tend to weaken the oxidizing bath.

The present invention solves the problem of oxidizing copper alloys ofthe class described by means of a predip which is used following thecustomary cleaning operation and just before immersion in the oxidizingbath.

The'predip used consists of an aqueous solution of sodium or potassiumhydroxide and sodium or potassium bromate.

The pieces to be blackened are immersed in the predip solution with atemperature ranging from 210 to the boiling point of the solution. Afterfrom three to fifteen minutes immersion, the surface color changes to abrownish color in the range from grey-brown to purple-brown, dependingon the alloy. When the surface color is uniform, the parts are rinsedand transferred to the oxidizing bath where they rapidly require thedesired black oxide finish. Copper alloys of the class describedimpossible to oxidize directly may be colored by this method, and alloysso processed will not excessively weaken the oxidizing bath. Anotheradvantage of this method is that total finishing time is substantiallyreduced.

A satisfactory predip is an aqueous solution consisting essentially ofan alkali selected from the group comprising sodium hydroxide and p0-tassium hydroxide and of an oxidizing agent selected from the groupcomprising sodium bromate and potassium bromate. Sodium hydroxide ratherthan potassium hydroxide is ordinarily preferred and potassium bromaterather than sodium bromate is ordinarily preferred, but the invention isnot so limited. The concentration may advantageously be g./l. hydroxideand 100 g./l. bromate, but the concentration is not critical and mayrange from 10 g./l. hydroxide and 15 g./1. bromate to 800 g./l.hydroxide and 400 g./l bromate The concentration may be adjusted to bestmeet the requirements of the alloy being processed. The solution ismaintained at a temperature at or just below the boiling point. Thesolution is stable with satisfactory life. There is no gassing and noharmful fumes are generated.

A composition conforming to the invention and adapted for making apredip solution incorporating the invention consists essentially of analkali selected from the group comprising sodium hydroxide and potassiumhydroxide and of an oxidizing agent selected from the group comprisingsodium bromate and potassium bromate.

In such a composition the ratios of the hydroxide to the bromate mayrange from 2:3 for weak solutions and 2:1 for strong solutions.

The present invention is not limited to the coating of copper alloys,but may be used to coat surfaces of other metals which have been platedwith a copper alloy.

The invention claimed is:

1. The'proce's's "of preparing a'copperl base alloy for black surfaceoxidization, the process-comprising immersing the alloy in an aqueoussolution which is approximately at the boiling temperature and whichconsists essentially of an alkali selected from the groupcomprisingsodium hydroxide and potassium hydroxide fandwiofrrlanzoxidizing agent selected from thegrqupi comprising sodium bromate andpotassium bromategthe concentration of the solution ranging from g./l.hydroxide and g./l. bromate to 800 gz/l. hydroxide and 400 g./l.,bromate, and continuing the immersion until the surf ace;color of; thealloy iscuniformly changed to a brownishcolor in the range fromgrey-brown to purple-brown.

2.- The process of preparing a copper base alloy =for-black-surfaceoxidization', the process -comprisingimmersing the alloy in anaqueous-solution which; is approximately at the boiling temperature andwhich consists essentially of' an alkali selected fromthegroup-comprising sodium hydroxide andpotassium-hydro-xide andxof' anoxidizing agent selectedfrom the group; comprising sodium bromate andpotassium bromate, the concentration of the solution being approximately100 g./1= hydroxide and 100 g;/l-. bromate,

and-continuingthe immersion until thesurfac-e color of the alloy isuniformlywchanged to a brownish color in the range-from grey-brown topurple-brown.

3.- The process-of preparing a copper'base-alloy fOIr-blflCk surfaceoxidization, the processwomprising immersing the alloy inanaqueoussolution which is; approximately at the b0i1ingrtem 'perature and whichconsists essentially of-sodium hydroxide and :potassium bromate, ;the"con- :centration {of the solution ranging from 10; g., l-.

a copper base alloy, the process comprising immersing the alloy in anaqueous solution which is approximately at the boiling temperature and-ide and l5gL/1: bromate-to 80G g./l.hydroxide and 400 g./l. bromate,continuing the immersion auntil the surface color of the alloy isuniformly changed-to a, brownish color in the range from 'grey b'rown topurple-brown, and thereafter imnlersingilthenalloy in a second hotaqueous solution consisting essentially of an alkali selected from-thegroup comprising sodium hydroxide and potassium hydroxide and of achlorite selected froniIthe-group comprising sodium chlorite andpotassium chlorite.

v5. 'Ihe;process of producing a black surface on a copper'base alloy,theprocess comprising immersing the alloy in an aqueous solution whichis approximately at the boiling temperature and whichconsistsessentially of an alkali selected from the group comprisingsodium hydroxide and potassium hydroxide and of an oxidizing agent?selected from the group comprising sodium bromate and potassium bromate,the concentration of-the solution being approximately g./l. hydroxideand100 g./1. bromate, continuing-the immersion until the surface color ofthe alloy is uniformly changed to a brownish color in the rangefrom-grey-brown to. purple-brown, and thereafter-immersing the alloy ina second hot aqueous solution consisting essentially of an alkaliselected from the group comprising sodium hydroxide and potassiumhydroxide and of a chlorite selected from the group comprising sodiumchlorite and potassium chlorite.

EARLE B. LEWIS.

. REFERENCES CITED The following references are of record in the file ofthis patent:

. UNITED STATES PATENTS Number Name Date 2,317,205 LoWit Apr. 20, 19432,364,993 Meyer Dec. 12, 1944 Certificate of Correction Patent No.2,457,480. December 28, 1948.

EARLE B. LEWIS It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 1, line 33, for oxidation read oxidization; column 2, line 20,for require read acquire; and that the said Letters Patent should beread with these corrections therein that the same may conform to therecord of the case in the Patent Office.

Signed and sealed this 12th day of April, A. D. 1949.

THOMAS F. MURPHY,

Assistant Gommz'ssz'oner of Patents.

Certificate of Correction Patent No. 2,457,480. December 28, 1948.

EARLE B. LEWIS It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows:

Column 1, line 33, for oxidation read oxidization; column 2, line 20,for require read acquire and that the said Letters Patent should be readwith these corrections therein that the same may conform to the recordof the case in the Patent Oflice.

Signed and sealed this 12th day of April, A. D. 1949.

THQMAS F. MURPHY,

Assistant Gammissz'oner of Patents.

